Legions Unleashed: 5 Battles That Made the Roman Empire

In the first century BCE, a series of civil wars tore the Roman Republic apart. However, instead of falling into ruins, ancient Rome was transformed into an even more powerful state — the Roman Empire.

The first Roman emperor, Augustus, carried out a reform of the imperial military. This professional standing army, consisting of up to 26 legions at any given time and backed by a large number of auxiliary forces, was transferred to the distant frontiers. The only military unit left in Italy was the newly established Praetorian Guard, the emperor’s personal bodyguard. Having eliminated a potential new civil war, Augustus could focus on a policy of expansion. However, his first attempt to push the frontier over the Rhine, and conquer Germania, failed spectacularly.

Augustus’ heirs were more successful. During the first and second centuries CE, the Roman Empire extended its territory both West and East, establishing imperial rule in Britain, Dacia, Arabia, and Mesopotamia. The expansion was halted in the mid-second century when the first signs of trouble appeared on the horizon, and barbarian tribes crossed the frontier. Here are five key battles from the early imperial era, during which time the Roman legions dominated the ancient world.

One of the most famous battles fought by the Roman Empire — the Battle of Teutoburg Forest — was also one of its worst defeats. At the beginning of the 1st century CE, the frontier of the young Roman Empire in Northern Europe was extended across the Rhine, towards the Weser and Elbe rivers. After almost two decades of combat, the Romans were in the advanced stage of turning these untamed lands into a frontier province, known as Germania. Yet, several Germanic tribes were unwilling to give up. When emperor Augustus withdrew eight of his legions and his best general (and future heir) Tiberius to crush a revolt in Illyricum, the barbarians decided to act.

Following the withdrawal of most of the Roman forces, command of the remaining troops in the area was given to the newly appointed governor of Germania, Publius Quinctilius Varus. Varus was left in command of three legions — the Seventeenth, the Eighteenth, and the Nineteenth — accompanied by Germanic auxiliaries. The leader of the auxiliaries of the Cherusci tribe was Arminius, a Germanic prince who had distinguished himself fighting for the Romans. However, unbeknownst to the Romans, Arminius was secretly harboring forces, and preparing to deal the Romans one of the most humiliating defeats in the Empire’s history.

In the Summer of 9 CE, Varus was conducting a pacifying operation east of the Weser River in central Germany. When Arminius informed him of the supposed rebellion in the northwest reaches of Germania, the Roman commander took all three legions and quickly set out westward. Despite the warnings of Arminius’ treachery, Varus trusted his old ally, marching his army into the vast and hard-to-traverse Teutoburg forest. Varus’ army was an imposing force, around 20, 000 strong. But the Roman column, more than ten kilometers long and encumbered by a long train of baggage and camp followers, was an easy target.

When the army entered the forest, Arminius and his men abandoned the Romans, proving that the earlier rumors were well-founded. It was too late. Arminius’ warriors, bolstered by the arrival of their Germanic allies, attacked the vulnerable Roman column. The Romans, unable to form a battle formation, could offer only a limited resistance and fell easy prey to the better-prepared enemy. The defenders were hampered by the heavily forested and muddy terrain, which offered no natural obstacle. To make things worse, the weather was appalling.

For four days, the barbarians fought the Romans and their hit and run tactics made progress almost impossible. The column may have split in two at some point, resulting in even greater chaos among the legionaries. Those who managed to reach open terrain became victims of the barbarian cavalry. When the fourth day of fighting came to an end, most of the Roman soldiers were killed, and all three veteran legions were annihilated. Varus, confronted with the staggering loss, committed suicide. News of the disaster shocked the elderly Emperor Augustus, who reportedly wandered around his palace shouting: “Quinctilius Varus, give me back my legions!” Six years later, the Roman forces returned to punish the Germanic tribes, but plans to advance eastwards were abandoned for good. The lands beyond the Rhine would remain permanently outside of the Roman Empire.

Following emperor Claudius’ invasion in 43 CE, much of Britain had become a Roman province. However, when it looked like the isle was firmly under imperial control, a revolt broke out, threatening to topple the Roman government. Unlike at Teutoburg, the imperial legions managed to recover from the brink of defeat. Then, the Roman Empire struck back, defeating the rebel queen, and eliminating all hostile opposition. The Battle of Watling Street secured Rome’s control over Britain, which would last for almost four centuries.

The unusually named battle took place in 61 CE, at a pivotal moment in the Roman occupation of Britain. The uprising — known as the revolt of Boudica — broke out after the famous queen of the Iceni had been brutally treated by the local imperial authorities. The neighboring tribes soon joined Boudica and her people. The revolt caught the Romans unprepared. With the bulk of the Roman forces away on campaign in northwestern Wales, the rebel army stormed and sacked several major Roman towns, including Camulodunum (Colchester), Verulamium, and the provincial capital, Londinium, modern-day London.

At the Battle of Camulodunum, the barbarians completely destroyed a large vexillation (detachment) of the Ninth Legion. More than 2,000 Romans died in the attack, further hampering the imperial response to this grave threat. To prevent the total collapse of Roman rule in Britain, it was paramount to react swiftly and defeat Boudica and her growing army. The task fell to Gaius Suetonius Paulinus, the governor of Roman Britain. Hearing the news about the ongoing disaster, he swiftly marched back from Wales at the head of the Fourteenth Legion. To this, Paulinus added detachments from the Twentieth Legion and all available auxiliaries. The Second “Augusta”, based in Exeter, was available, but its commander declined to join.

Suetonius was now in command of almost ten thousand men. While this was not a small number, Paulinus had to confront a much larger hostile force numbering around 100,000. The Romans took a stand at an unknown location, somewhere along the Roman road known as Watling Street. Paulinus, aware that he was heavily outnumbered, positioned his troops in a defile between wooded hills, an easily defensible location.

Although great in number, the Britons lacked armor, organization, and the superior discipline of the Roman legions. In addition, well-trained Roman soldiers fared much better in close combat than Boudica’s warriors. The result was a disaster. Paulus’ legionaries waited until the enemy was almost upon them. Then, on command, the soldiers threw their pila and marched in a wedge-shaped formation, cutting the enemy to pieces. Once the Britons were in disarray, Paulinus ordered a cavalry charge. Thousands of barbarians were cut down by the Romans as defeat turned into a rout. Their families, who assembled to watch the battle, also died or were taken into slavery.

Queen Boudica fled the battlefield but died soon afterward, poisoning herself or succumbing to illness. The victory at Watling Street secured Roman Britain, allowing Emperor Nero to continue colonization. Despite minor revolts in the north, Britain would remain an important province of the Roman Empire until the early 5th century.

While the Roman Empire enjoyed relative peace during its first century, the legions had to quell occasional revolts. One of the most famous uprisings against imperial rule happened in 66 CE when the province of Judea rebelled against Rome. The suppression of the revolt fell into the hands of the future emperor Vespasian and his son Titus. However, three years later, Vespasian departed for Rome, and after a short but bloody civil war, was appointed as the new Roman emperor. Titus took command of the army in his father’s absence, and in 70 CE, the vengeful Roman legions conquered Jerusalem, razing the holiest place of the Jews, the Second Temple, to the ground. Yet, Judea was not wholly pacified.

While most of the rebels were killed or enslaved, a small number of zealots were able to flee Rome’s wrath. Some of those who escaped, led by one Elezar ben Yair, reached the safety of the imposing mountaintop fortress of Masada. Situated on the flat plateau on top of the steep-sided rocky hill near the coast of the Dead Sea, Masada was considered impregnable. The fortifications date back to the second century BCE, but the bastion defenses had recently been bolstered, under Herod I, the Roman appointed king of Judaea.

The Romans could not ignore the rebels’ defiance, and in November 73 CE, the Tenth Legion “Fretensis” laid siege to Masada, encircling the mountain with walls, towers, and camps. The blockade, however, would be a lengthy and costly business. Large storehouses and water cisterns in the fort meant that those inside would be able to survive the several-year-long siege. So instead, the Romans devised a remarkable plan to take the fortress by direct assault. The soldiers set about building a massive earth ramp on the western side of the hill.

Built under constant fire by the enemy’s catapults, the ramp, when completed, was a marvel to behold. Over 600 meters (2,000 feet) long and 61 meters (200 feet) high, the ramp was large enough to push a siege tower up. Equipped with a ram on its lower tower and a ballista on the top floor, the siege engine soon breached the fortress wall. However, when the Romans stormed the fortress, they found that the defenders had committed mass suicide, preferring death at their own hands to slavery or execution. According to the eyewitnesses, only two women and five children survived out of 960. Recent research questions that story, but it is undebatable that the Romans achieved a great victory having taken the fort.

Masada was the last act of the First Jewish-Roman War and a lesson to everyone who dared to rebel against the Empire. Despite the defeat, tensions would continue to brew in the region. In the early second century, during the reign of Emperor Hadrian, the Jews rose again. This time, the Roman response would be horrific. Following the end of the third uprising (the Bar Kokhba Revolt) the Jews would be expelled from the province and resettled around the Mediterranean. Judaism would be forbidden for a while, while the city of Jerusalem was briefly renamed Aelia Capitolina. Although Hadrian’s death eased restrictions and persecutions, the Jewish population in the region would remain significantly reduced up to the mid-20th century.

Besides quelling revolts during the early Roman Empire, the legions were primarily employed in offensive operations. The addition of valuable wealthy and strategic regions, from Europe to Asia, nearly doubled the imperial territory, further bolstering the Empire’s strength and influence. It was under Emperor Trajan that Rome reached its apex, becoming the most powerful state in the world. Perhaps the most important of Trajan’s conquests was a vast and rich area north of the Danube, known as Dacia. In two bloody wars, the imperial legions, led by Trajan himself, weakened and destroyed the mighty Dacian Kingdom. The wars and battles fought between 101-102 and 105-106 CE were immortalized in the reliefs on the famous Trajan’s column, which still stands in the heart of the city of Rome today as an eyewitness to the splendid victory.

For centuries, the Dacians were a regional power, raiding and exacting tribute from neighboring tribes. These warlike people ruled over the region north of the Lower Danube, the area roughly corresponding to the territory of present-day Romania. In the last decade of the first century CE, the Dacians, led by their king, Decebalus, carried out raids across the Danube into territory belonging to the Roman Empire. Although the result was a peace treaty favorable to the Dacians, the incursion into the imperial territory would soon prove to be a grave mistake.

Following the assassination of the last Flavian, Domitian, and the end of Nerva’s short rule, the new Roman emperor, Trajan, decided to carry out a punitive expedition into Dacia. Trajan, who before taking the purple distinguished himself on several battlefields, was popular with the army. Thus, it is not surprising that the Dacian campaign was received with great enthusiasm by the soldiers. In 101 CE, Trajan personally led an army of nine legions, around 45,000 strong, as well as a large number of auxiliaries, across the Danube. The crossing itself was an impressive undertaking. The legionaries crossed the great river over the bridge of boats. Little is known about the course of the campaign, but there was clearly a lot of bloodshed. In early 102, Decebalus was forced to concede defeat and accept Rome’s terms.

However, three years later, Decebalus resumed raids on Roman territory. Trajan returned with a vengeance. This time, the emperor was determined to conquer the unruly land. His soldiers built the largest bridge of the ancient world, a marvel of engineering, across the broad expanse of the Danube. After reaching the other side of the river, the Roman legions thrust into the Carpathian mountain region to besiege the Dacian capital of Sarmizegethusa. Following a long siege and string of Roman victories, the besieged Dacians committed mass suicide. Decebalus managed to escape but slit his own throat when tracked down by Roman scouts.

Following the destruction of the enemy force, and the sack of their capital and holy places, Trajan annexed the wealthy region. Dacia, the once-mighty kingdom, was no more. Rome was now in possession of the fertile province and the renowned Dacian gold mines. The emperor celebrated his victory with the erection of the famed Trajan’s column. Subsequent campaigns in Arabia, Armenia, Assyria, and Mesopotamia, would ensure that Rome reached its greatest extent under Trajan’s rule.

When Marcus Aurelius and his adoptive brother Lucius Verus took the reins of the Roman Empire in 161 CE, no one could have expected the series of calamities that would mark their reigns. Their early successes in the Parthian War were quickly overshadowed by the Antonine plague, which in 15 years took between 5-10 million lives, probably claiming the life of Emperor Verus himself. Then, in the early 160s, disturbing rumors from the Danubian frontier reached the capital of destroyed frontier posts, manpower losses, and a mysterious threat looming on the horizon.

Letters from the northern frontier were a portent of decades of bloody warfare, which would occupy the rest of Marcus Aurelius’ reign and which would see a Roman emperor for the first time in centuries leading a defensive war. In 166 CE, the Danubian limes collapsed under the attack of the powerful Marcomanni tribe, who crossed the great river, accompanied by other Germanic tribes. Soon they were followed by the Sarmatian Iazyges and other warlike peoples. While Marcus Aurelius was able to repulse some of these attacks, the multiple breaches of the limes hampered an effective defense. In addition, the strength and numbers of the frontier legions were depleted by the ongoing plague, significantly reducing Rome’s military capabilities. Thus, the barbarians penetrated deep into the Roman Empire’s interior, reaching as far as Greece.

The worst was yet to come. In 170 CE, at the Battle of Carnuntum (near modern-day Vienna), the Marcomanni and the Quadi won a decisive victory over a force of 20,000 Roman soldiers. Defeat of such a magnitude left the gateway to Italy open. For the first time in more than three centuries, barbarians entered the imperial heartland. Marching into the Po Valley unopposed, the barbarians plundered and razed Opitergium (Oderzo), and began besieging the major Italian city of Aquileia. The panic that gripped Rome resulted in defensive perimeters being built around the main towns in the peninsula. Thankfully, the emperor proved to be a competent planner and commander. By 171, Aquileia was relieved, and after several diplomatic talks with various tribes, the Romans managed to isolate the Marcomanni.

In 172, Marcus Aurelius, leading an army, mostly composed of the eastern legions, crossed the Danube into Marcomannic territory. The following year, the Romans almost lost the critical battle in what is known as “The Rain Miracle”. Overwhelmed by the large Quadi force, the Twelfth Legion “Fulminata” (“Thundering”), faced certain destruction due to a lack of water. However, when disaster seemed inevitable, a sudden torrential thunderstorm saved the Romans. While the legionaries satiated their thirst, lightning struck the Quadi. By 174, the subjugation of the Quadi was complete, and the next year the imperial forces defeated the Sarmatians. In 176, together with his son Commodus, the emperor visited Rome for the first time in years, celebrating a joint triumph. The Aurelian column still stands as a witness to the grand victory.

But the trouble was not over yet. Two more Marcomannic Wars would follow, although the Roman Empire would not find itself in as grave a danger as during the first conflict. After suppressing an internal revolt in the East, the emperor returned to the Danubian border. In 180, Marcus Aurelius, the last of the “Five Good Emperors,” died in the army camp, leaving the Roman Empire to his son. Commodus, however, was not interested in pursuing the war, negotiating a peace treaty with both the Marcomanni and the Quadi, and departing to Rome to celebrate his own triumph. In mid-182, the final operations against the Sarmatian tribes on the lower Danube were completed, restoring peace along with the entire limes. Yet, the Germanic tribes were only temporarily checked; the Marcomannic wars were a prelude to the invasions and chaos that would engulf the Roman Empire in the following century, eventually leading to the fragmentation of the Roman West in the late fifth century.